Clay Nanotubes Aligned with Shear Forces for Mesenchymal Stem Cell Patterning

Aligned halloysite nanotubes on solid substrates are fabricated by a shearing method with brush assistance. These clay nanotubes are aligned by shear force in strip-like patterns accomplished with drying ordering at elevated temperatures. The nanotubes' orientation is governed by "coffee-ring" formation mechanisms depending on the dispersion concentration, nanotube charge, and speed of thermos-evaporation. Polarized light irradiated through the patterns demonstrates birefringence and confirms the orientation. Scanning electron microscopy and atomic force microscopy show that the nanotubes are aligned along the direction of the wetting lines above 4 wt%, while they are not oriented at lower concentrations. Halloysite concentration, drying temperature, and type of brush fibers affect the pattern ordering. The aligned halloysite systems on glass, tissue culture plates, and polymer films, provide a promising platform for biocell guiding. Human foreskin fibroblasts proliferated well on the aligned clay patterns and the cell orientation agrees with the nanotube direction. Human bone mesenchymal stem cells (HBMSCs) are also cultured on the organized halloysite coating. The clay patterns support HBMSC proliferation with alignment, and such nanostructured substrates promote osteogenesis differentiation without growth factors. This facile method for preparing aligned halloysite patterns on solid substrates is very promising for surface modification in biotissue engineering.